Let's suppose that the results of that study are accurate and generalizable, so that (1) teachers with at most two years of experience are dramatically worse th

Let's suppose that the results of that study are accurate and generalizable, so that (1) teachers with at most two years of experience are dramatically worse than ones with three or more, but that beyond that there's no advantage to having more. And let's suppose that although the study talks about "less than three years experience" and is written as if there's no such thing as a teacher with less than one year of experience, what they actually mean is "first two years", "next two years", etc. So. You are proposing to throw teachers out after six years of teaching. Then, assuming every teacher stays the full six years, 1/3 of all teachers will be in that low-experience category that teaches so much less effectively. At present, according to the study you cited, the figure is more like 1/5. It seems that your proposal will result in 65% more pupils being taught by teachers who do not do a good job. This is not the only reason why your suggestion seems to me unlikely to be a good one, but it seems a pretty compelling reason.